We can use User.class.getConstructors() and find there are 2 constructors , and with constructor.getParameterTypes() , we can identify there's one constructor with two String parameters.
We can also use reflection to find two properties : username and password.
But , at run time , we don't know the proper sequence of the two parameters being used to call constructor.newInstance(?,?).

constructor.newInstance(username , password) , and constructor.newInstance(password , username) are both legal but with totally different result.

I cannot use User.class.newInstance() and set property value because the no-arg constructor is protected.

I encounter this problem because I am trying to write a generic JPA CRUD tool. List/Read/Update/Delete are OK. But now I face the problem that I cannot online create an object. The entity classes are all with a protected no-arg constructor (so I cannot use class.newInstance()) , and one a-lot-of-parameter public constructor (but the parameter names are erased at runtime).

How to do this ? Does javassist or other proxy-techniques help ? how ?
Thanks a lot !